This invention relates generally to the coating of a cylindrical elongated object with a cementitious mortar, and, more specifically, to the coating of the inside surface of a cast iron pipe with a high alumina cement. The cast iron pipe may be made of either gray iron or ductile iron. The cement may utilize a plasticizer such as fireclay, and also is coated with an asphaltic based coming prior to curing.
It is known to line the interior surface of cast iron pipe with a cementitious mortar or cement lining for the transmission of potable water, such cement lining also may be coated with an asphaltic based coating. Because exposure to potable water is not as severe service as exposure to sewage, the major concern with such cement and asphaltic based coated cast iron pipe is corrosion protection. Accordingly, the major goal is to provide a substantially crack free and void spot free cement lining and also an impervious coating on such cement lining. However, in applications of such lined cast iron pipe for sewer use, the exposure environment is quite more severe and the potential for an acidic environment, in the low pH range, is possible. Accordingly, the concerns about corrosion increase tremendously in such service.
It is also known to line the interior of cast iron pipes with calcium alumina cement. However, such cement linings are known to be prone to cracking leading to corrosion of the cast iron pipe, especially in a sewer environment.
In response to the demands of such sewer service, some cast iron pipes for such service have been lined with a plastic or polyethylene coating. Such a coating can provide good resistance to corrosion, but is quite expensive. There is also a concern regarding the ability of such plastic linings to adhere to the internal surface of the cast iron pipe. However, even such plastic lined pipe is subject to small void spots or discontinuities which can permit the acid environment to contact the cast iron pipe and thereby lead to corrosion.
One solution to this problem is disclosed in U.S. Pat. No. 5,037,600, which discloses the lining of a cast iron pipe with a polyolefin-cement mixture thereby assuring the adherence of the mixture to the internal surface of the pipe. A second polyolefin coating is then applied on top of the polyolefin-cement mixture to complete the lining. Such a lining arrangement has shown to be successful, but is rather expensive to produce.
Another problem with such mixtures is the need to treat the ends of the pipe which are joined in well-known gasket type joints. The tolerances in such pipe end joints are such that the cement coating cannot be applied to the interior of the pipe bell and still leave the bell capable of accepting the end from the adjoining pipe.